Composition and method for polishing rigid disks

ABSTRACT

A method for polishing computer rigid disks comprising bringing at least one surface of the rigid disk into contact with a polishing pad and applying a composition to the rigid disk comprising at least one hydroxylamine additive and colloidal silica to give a polished rigid disk.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns polishing compositions and methods for using thepolishing compositions to polish rigid disks. The compositions generallyinclude colloidal silica and at least one hydroxylamine polishingadditive. More particularly the compositions and method of thisinvention are adapted for polishing electroless nickel deposited rigiddisks that are used in computer hard drives.

2. Description of the Related Art

There exists a continuing desire to miniaturize electronic componentsused in the computer and electronics industries. The driving force forminiaturization in rigid disks is similar to that in the semiconductorindustry. Customers are demanding continually increasing storagecapacity in rigid disks. At the same time the design rules used bycomputer manufacturers call for smaller hard drives. The only solutionavailable to rigid disk manufacturers is to increase the storage densityof the magnetic media.

Miniaturization has created component quality concerns, many of whichare resolved by the precise polishing of computer and electronicsubstrate materials for magnetic disks and semiconductors. As a result,identifying methods and compositions that can produce an essentiallydefect free electronic substrate surface has become crucial in themanufacture of smaller and smaller computer and electronic substrates.

Dispersions and chemical mechanical polishing (CMP) slurries have beendeveloped for use in conjunction with semiconductor device manufacture.However, few of the commercially available dispersions or CMP slurrieshave been evaluated in rigid disk polishing applications. For example,U.S. Pat. No. 4,475,981 discloses polishing the metal surface of nickelplated blanks for rigid memory disks with a composition including cericoxide or aluminum oxide powder, a water soluble chlorine-containing mildoxidizing agent and an aqueous suspension of colloidal alumina oxide orceria oxide. U.S. Pat. Nos. 4,696,697 and 4,769,046, each disclosemethods for polishing memory disks using an abrasive compositionincluding alpha-aluminum oxide and a polishing accelerator such asnickel sulfate. The aluminum oxide polishing agent preferably has aminum particle size of 0.7-4 μm and a maximum particle size of 20 μm orless. U.S. Pat. Nos. 4,915,710 and 4,929,257 each disclose abrasivecompositions suitable for polishing aluminum based substrates formagnetic recording disks. The composition disclosed includes an aluminaabrasive, a polishing accelerator such as gluconic or lactic acid andcolloidal alumina. In addition, U.S. Pat. No. 5,527,423 discloses anabrasive composition that is particularly useful in the method of thisinvention. Likewise, U.S. patent application Ser. No. 08/753,482,incorporated herein by reference, discloses a chemical mechanicalabrasive composition including an oxidizer and a catalyst that is usefulin the method of this invention. Polishing compositions including analumina abrasive and a hydroxylamine additive are disclosed in U.S. Pat.No. 5,735,963.

Methods for polishing rigid disks are disclosed in U.S. Pat. Nos.4,769,046, 5,084,071, and 5,441,788 each of which are incorporatedherein by reference. U.S. Pat. No. 4,769,046 discloses a method forpolishing a layer of nickel plated on a rigid disk using a compositioncomprising aluminum oxide and a polishing accelerator such as nickelnitrate, aluminum nitrate, or mixtures thereof. U.S. Pat. No. 5,084,071discloses a method of chemical mechanical polishing and electroniccomponent using a composition including abrasive particles that are notalumina, a transition metal chelated salt, a solvent for the salt, and asmall but effective amount of alumina. Finally, U.S. Pat. No. 5,441,788discloses a method for manufacturing a nickel phosphor recording diskincluding polishing the NiP substrate to a surface roughness to no lessthan 2.0 nm RMS.

Commercially available rigid disk polishing slurries are unable to meetthe new rigid disk surface finish parameters. Furthermore, compositionsthat are presently known to be capable of polishing rigid disks areunable to polish rigid disks at a high rate and, at the same time,produce an acceptable surface finish. Therefore, there remains a needfor polishing compositions that are capable of polishing rigid or harddisks at high rates with low defectivity, while providing a smoothsurface finish.

SUMMARY OF THE INVENTION

The present invention is directed to compositions that are capable ofpolishing rigid disks at high rates with little or no increase in diskdefectivity.

The present invention is also directed to compositions that are usefulin conjunction with an abrasive polishing pad and/or in conjunction witha particulate abrasive for polishing electronic substrates.

The present invention is further directed to a method for removingnickel phosphide from an aluminum alloy-based rigid disk at high rateswith polishing compositions.

In one embodiment, this invention is a polishing composition comprisingwater and at least one hydroxylamine additive wherein the polishingcomposition is combined with aqueous colloidal silica to give apolishing slurry or wherein the colloidal silica is embedded or appliedto a polishing pad and thereafter the polishing composition is combinedwith the abrasive pad.

In still another embodiment, this invention is a method for polishing arigid disk. The method includes the steps of: (a) providing a polishingcomposition comprising water and at least one hydroxylamine additive;(b) applying the polishing composition to at least one surface of therigid disk; and (c) removing at least a portion of a metal layer fromthe rigid disk by bringing a polishing pad into contact with the surfaceof the rigid disk and moving the pad in relation to the rigid disk togive a polished rigid disk where colloidal silica is incorporated intothe polishing composition, the polishing pad or both.

DESCRIPTION OF THE CURRENT EMBODIMENT

The present invention relates to polishing compositions of matter usefulfor polishing rigid disks. The present invention also relates to amethod for polishing rigid disks using a polishing composition withspecific additives including colloidal silica and hydroxylamine. Inparticular, the polishing composition of the invention are capable ofpolishing rigid disks at good rates to give polished rigid disks havingexcellent RMS roughness of less than about 0.6 nm at polishing ratesgreater than about 1.5μ inch/min/side.

Before describing the details of the various preferred embodiments ofthis invention, terms that are used herein will be defined. The term“rigid disk” refers to rigid disks and hard disks, such as an aluminumdisk or nickel phosphor (NiP) plated aluminum disk upon which a magneticmedia for computer memories will be coated.

An aspect of this invention is a method for polishing rigid disks thatuses a polishing composition that has heretofore been unappreciated asbeing useful for polishing rigid disks. Polishing compositions usefulfor polishing rigid disks according to this invention include at leastone hydroxylamine additive and colloidal silica. The polishingcompositions of this invention may be combined with colloidal silica ina slurry to give a polishing composition that is useful for polishingrigid disks or the colloidal silica may be incorporated into a polishingpad and thereafter combined with an aqueous hydroxylamine solution.Examples of abrasive pads useful with polishing compositions of thisinvention are disclosed in U.S. Pat. Nos. 5,849,051 and 5,849,052 whichare incorporated herein by reference.

The polishing compositions of this invention include at least onehydroxylamine additive. The term hydroxylamine additive as used hereinrefers to hydroxylamine (NH₂OH), derivatives of hydroxylamine, andhydroxylamine salts including, for example, nitrate salts, sulfatesalts, phosphate salts and mixtures thereof. U.S. Pat. No. 5,735,963,the specification of which is incorporated herein by reference,discloses hydroxylamine derivatives and salts thereof that are useful inthe chemical mechanical polishing compositions of this invention.Preferred hydroxylamine additives include hydroxylamine, hydroxylaminenitrate, hydroxylamine sulfate, hydroxylamine phosphate and mixturesthereof. Most preferred hydroxylamine additives are hydroxylamine,hydroxylamine nitrate, and mixtures thereof.

One or more hydroxylamine additives may be present in a chemicalmechanical polishing compositions in an amount ranging from about 0.01to about 25.0 weight percent and preferably from about 0.01 to about10.0 weight percent. It is preferred that at least one hydroxylamineadditive is present in the compositions of this invention in amountsranging from about 0.01 to about 5.0 weight percent.

The polishing compositions of this invention may be combined with atleast one colloidal silica abrasive prior to using the composition topolish a substrate such as a rigid disk. The colloidal silica may beadded to the aqueous polishing composition to form an aqueous chemicalmechanical polishing slurry. Alternatively, the colloidal silica may beincorporated into a polishing pad during or following the manufacture ofthe polishing pad. Thereafter, the aqueous polishing composition may beapplied to a substrate being polished or directly to the polishing padsuch that the colloidal silica in the polishing pad and the aqueouspolishing composition work in unison to polish the substrate.

The colloidal silica abrasive may be any of a wide variety of aqueouscolloidal silicas or gels that are available commercially. Colloidalsilicas are stable dispersions of nanometer discrete silica particlessuspended in water or some other medium. The production of colloidalsilica is a well-known process which typically involves condensation andpolymerization of a silica sol. For purposes of this disclosure, theterm “colloidal silica” refers to small spherical silica particleshaving a mean particle size ranging from about 1 nm to about 200 nm thatare preferably manufactured by condensation and polymerizationprocesses. It is also preferred that essentially all of the colloidalsilica particles have a mean average particle size of from about 40 nmto about 120 nm and most preferably from about 50 nm to about 100 nm.Furthermore, essentially all of the colloidal silica particles will fallwithin a particle size range or from about 1 to 3000 nm and preferablyfrom about 5 to about 100 nm. The term “essentially all” means that atleast 75 % of the colloidal silica particles are within the statedrange.

The properties of several useful aqueous colloidal silicas are setsummarized in U.S. Pat. No. 4,588,421, the specification of which isincorporated herein by reference. Examples of useful colloidal silicasinclude colloidal silicas manufactured by Nalco, Naperville, Ill. andsold under the tradenames NALCO® 1115, NALCO® 2326, NALCO® 1130, NALCO®1030, NALCO® 1140, NALCO® 1934A, NALCO® 2327, NALCO® 1050, NALCO® 1060,NALCO® 2329, NALCO® 4291, and Bindzil 50/80 and Bindzil 40/170 eachmanufactured by Akzo Nobel.

The colloidal silica should be present in chemical mechanical polishingslurries of this invention in an amount ranging from about 0.5 to about25 wt %, more preferably from about 1.0 wt % to about 12 wt % and mostpreferably in an amount ranging from about 1.0 to about 6.0 wt %.

pH is an important property of the polishing compositions of thisinvention. Generally, the composition will have a pH from about 1.5 toabout 11.0. It is preferred that the pH ranges from about 2.0 to about5.0 and most preferably from about 3.0 to about 4.0.

Other well known polishing composition additives may be incorporatedalone or in combination into the polishing composition of thisinvention. A non-inclusive list of optional additives includes inorganicacids, organic acids, surfactants, alkyl ammonium salts or hydroxides,dispersing agents, oxidizing agents, additional abrasives, complexingagents, film forming agents and so forth.

The polishing machines used to manufacture polished rigid disks consistof a pair of platens. Both platens have the same size and can be rotatedin opposite directions independently. A pair of identical pads aremounted on both upper and lower platens. The upper platen and the upperpad have a series of holes in which the polishing composition or slurrycan be distributed evenly during the polishing. Depending on thespecific machine, 25 to 45 disks (95 mm OD) can be loaded on the lowerplaten at one time by putting them into several carriers. These carriershave tiers that can be fit into both inner and outer gears on the lowerplaten. There are three or four motors (depending on the specificmachine) which control the rotations of the platens and the carriers.

During the polishing, the upper and lower platens rotate in the oppositedirections. By controlling the relative speeds between inner and outergears, the carriers and the disks also rotate during the polishing.Therefore, both sides of the disks are polished evenly at the same time.For the second step polishing, the polishing time is typically 3 to 6minutes. The pressure on each disk during polishing is typically 0.8 to1.5 psi. The slurry flow rate is strongly dependent on the specificmachine.

Rigid disk polishing usually consists of two steps: first-step polishingand second-step polishing (or fine polishing). The first-step polishingremoves lots of the Ni-P materials on the rough surface of as-platedsubstrate. The resulting disks still have lots of scratches and otherdefects on the surface. Current technology requires defect-free andsmooth surface for maximum storage capacity. The purpose of the secondstep polishing is to eliminate all surface defects and generate smoothsurface. The compositions and polishing method of this invention areespecially formulated for the second-step polishing although they can beused in first step polishing if desired. Rigid disks polished usingmethods and compositions of this invention exhibit surface roughness ofless than about 0.6 nm and preferably less than 0.2 nm. In addition therigid disks are polished at a high rate, typically in the range of 1.5to 2.5 μinch/min/side or faster.

EXAMPLES

We have discovered compositions that are capable of polishing rigiddisks at high rates and with low defectivity.

The following examples illustrate preferred several embodiments of thisinvention as well as several preferred methods of this invention.

Example 1

Rigid disks polished in a first stage polishing step were obtained fromSeagate Technology. The rigid disks had a surface roughness of fromabout 30 to 50 Å. The rigid disks were polished with various abrasivecontaining polishing compositions. The rigid disks used werecommercially available nickel/phosphor (NiP) coated disks with aluminumsubstrates. The disks used in these experiments had all undergone apre-polishing.

The NiP coated aluminum rigid disks were polished using a table toppolishing machine manufactured by Streuers, West Lake, Ohio. The tabletop polishing machine consisted of a Rotopol 31 base and a Rotoforce 3downforce unit. Unless otherwise noted, twelve inch Polytex Hi pads,manufactured by Rodel, Inc. were used to polish the rigid disks in eachExample.

The rigid disks were polished for 10 minutes per side using a platenspeed of 150 rpm, a polisher carrier speed of 150 rpm, and a slurry flowrate of 100 ml/min. The polishing down force used was 50 Newtons. NiPremoval rates were calculated by weighing the clean, dry rigid diskprior polishing and following polishing and converting the weight lossto a thickness loss using a NiP density of 8.05.

The surface characteristics of the polished rigid disks were analyzedusing a TMS-2000 manufactured by Schmitt Measurement Systems, Inc. todetermine surface roughness (Å) and peak to valley (P-V) height (Å).

Example 2

In this Example, the testing method described in Example 1 was used toevaluate polishing compositions including various abrasives. Theabrasives evaluated included Bindzil 50/80 colloidal silica manufacturedby Akzo Nobel, NALCO® PR-4291 colloidal silica and NALCO® 2329 colloidalsilica each manufactured by Nalco, CAB-O-SPERSE®, SC-E fumed silicadispersion manufactured by Cabot Corporation, and SEMI-SPERSE® W-A355fumed alumina dispersion manufactured by Cabot Corporation. Each of thecompositions further included 0.25 wt % hydroxylamine nitrate. Thepolishing results are set forth in Table 1 below.

TABLE 1 Run % Rate Roughness P-V # Solids Type Solids pH (μm/min)Comments (A) (A) 1 Bindzil 50/80 4 4 3.25 No defects 2.17 22.7(Colloidal silica) observed 2 Bindzil 50/80 4 4 3.03 No defects 2.0318.7 (Colloidal silica) observed 3 Nalco PR-4291 4 3.5 3.60 No defects2.23 20.1 (Colloidal silica) observed 4 Nalco PR-4291 4 3.5 3.92 Nodefects 1.80 18.7 (Colloidal silica) observed 5 Nalco 2329 4 3.4 4.38 Nodefects 2.47 21.1 (Colloidal silica) observed 6 Nalco 2329 4 3.4 4.17 Nodefects 2.59 20.3 (Colloidal silica) observed 7 SC-E Cabot fumed 4 3.00.44 pits & 31.6 1236 silica highly concentrated particles 8 SC-E Cabotfumed 4 3.0 0.46 pits & 36.7 1521 silica highly concentrated particles 9W-A355 Cabot 1.5 4.0 7.93 visible pits 5.45  153 fumed alumina 10 W-A355Cabot 1.5 4.0 8.56 visible pits 8.92  534 fumed alumina

The polishing results show that the polishing abrasive is critical toachieving a good removal rate and a good surface finish. Specifically,the results indicate that polishing slurries including colloidal silica(runs 1-6) produced rigid disks with a uniformly polished surface atadequate removal rates. In contrast, compositions with filmed silicaabrasives (runs 7-8) polished rigid disks with high defectivity at muchlower rates than polishing compositions including colloidal silica.Compositions with fumed alumina on the other hand (runs 9-10) exhibitedthe highest removal rates and the worst defectivity results.

Example 3

In this Example, the polishing and testing methods described in Example1 were used to evaluate the performance of polishing compositionsincluding various colloidal silica abrasives. The polishing compositionsused and the polishing results are reported in table 2, below.

TABLE 2 Comments - Peak to % Rate Olympus Roughness Valley Run # SolidsType Solids pH Oxidizer (μin/min) observations* (A) (A) 1 Bindzil 50/804 4 0.25% hydroxylamine 3.25 No Defects 2.17 22.7 nitrate Observed 2Bindzil 50/80 4 4 0.25% hydroxylamine 3.03 No Defects 2.03 18.7 nitrateObserved 3 Nalco PR-4291 4 3.5 0.25% hydroxylamine 3.60 No Defects 2.2320.1 nitrate Observed 4 Nalco PR-4291 4 3.5 0.25% hydroxylamine 3.92 NoDefects 1.80 18.7 nitrate Observed 5 Nalco 2329 4 3.4 0.25%hydroxylamine 4.38 No Defects 2.47 21.1 nitrate Observed 6 Nalco 2329 43.4 0.25% hydroxylamine 4.17 No Defects 2.59 20.9 nitrate Observed 7Nalco 1050 4 3.2 0.25% hydroxylamine 1.42 No Defects 2.05 31.3 nitrateObserved 8 Nalco 1050 4 3.2 0.25% hydroxylamine 1.01 No Defects 1.8616.5 nitrate Observed 9 Nalco 1060 4 3.4 0.25% hydroxylamine 2.58 NoDefects 1.81 16.4 nitrate Observed 10 Nalco 1060 4 3.4 0.25%hydroxylamine 2.91 No Defects 1.81 16.6 nitrate Observed 11 Bindzil50/80 5 4 0.25% hydroxylamine 3.52 No Defects 1.9 20.9 flitrate Observed12 Bindzil 50/80 5 4 0.25% hydroxylamine 3.28 No Defects 1.8 10.7nitrate Observed 13 Bindzil 40/170 5 4 0.25% hydroxylamine 2.09 NoDefects 1.7 19.0 nitrate Observed 14 Bindzil 40/170 5 4 0.25%hydroxylamine 1.89 No Defects 1.7 16.6 nitrate Observed

What we claim is:
 1. A polishing composition comprising: water; fromabout 0.01 to 0.25 wt % of at least one hydroxylamine additive; andcolloidal silica.
 2. The chemical mechanical polishing composition ofclaim 1 having a pH of from about 2 to about
 5. 3. The polishingcomposition of claim 1 including from about 0.5 wt % to about 25 wt % ofcolloidal silica.
 4. The polishing composition of claim 1 including fromabout 1.0 to about 6.0 wt % colloidal silica.
 5. The polishingcomposition of claim 1 wherein the hydroxylamine additive is selectedfrom hydroxylamine, hydroxylamine salts and mixtures thereof.
 6. Thepolishing composition of claim 5 wherein the hydroxylamine salt ishydroxylamine nitrate.
 7. A chemical mechanical polishing compositioncomprising; water; from about 0.01 to 0.25 wt % hydroxylamine nitrate;and from about 1.0 to about 6.0 wt % colloidal silica.
 8. The chemicalmechanical polishing composition of claim 7 wherein the chemicalmechanical polishing composition has a pH of from about 2.0 to about5.0.